Sea urchins can scrape their way through solid rock to make themselves homes. This ability has long been suspected but never demonstrated, until now.

at Villanova University in Pennsylvania and his colleagues studied purple sea urchins (), which live along the west coast of North America. These animals look like purple balls with hundreds of spines. They also have structures called tubefeet, which they use to walk and move food to their mouths. They also use their tubefeet to attach themselves to rock, making it difficult to dislodge them. The safest homes are pits and holes, which offer a larger surface area for an urchin to lock onto.

In the lab, the researchers placed single sea urchins on flat pieces of soft mudstone, moderately hard sandstone and tough granite. After a year, they measured the weights of the rocks, how the surfaces looked, and how much the rocks were eroded.

The sea urchins had eaten holes in all the rocks, although they made slower progress on the harder ones. Field measurements showed that holes in mudstone were about 220 cubic centimetres, whereas holes in sandstone were 63 cubic centimetres and holes in granite were just 45 cubic centimetres.

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“We were not surprised that they excavate rock,” says Russell. “What shocked us was… how fast they were able to form pits, particularly in the sandstone.”

Russell says the sea urchins’ drilling abilities are a by-product of how they eat. Each animal has five sharp teeth on its underside. Even when they are not chewing on food, the teeth are constantly scraping the rock they sit on, sculpting it in the process. The urchins eat the rock scrapings.

The team calculates that sea urchins can create an immense amount of sediment every year: perhaps 200 tonnes per hectare. That is comparable to the amount of sediment carried to the sea by many rivers.

The sea urchins’ drilling may significantly erode rocky reefs in the temperate seas where they live. However, unlike voracious tropical sea urchins, they may be too slow to be a cause for concern, says of California State University, Sacramento.

Imagine you could teleport to any forest on Earth. When you land, you have a 50 per cent chance of being within half a kilometre of the forest’s edge. That is how badly our planet’s forests have been sliced and diced.

A new study shows that 85 per cent of animals are being affected by living in these dismembered forests. The findings will help conservationists figure out how best to protect these species.

While the fragmentation of forests is known to affect biodiversity and ecosystems, the effects studied so far are local and specific to particular species, making for a chaotic picture. of Newcastle University in the UK and her colleagues came up with a new method to make sense of the data.

Instead of simply separating regions into forest and non-forest, they also took into account changes to the land that surrounds the forests. Using existing population data, they mapped the abundances of 1673 vertebrate species – including amphibians, reptiles, birds and mammals – in 22 tropical regions in the Americas, Asia and Africa. These included many threatened species such as the and .

Of the species whose abundance changed near forest edges, 46 per cent have become more abundant over the last few decades, compared with 39 per cent that became less abundant. This may be good news for some species, although life on the forest edge may well change their behaviours.

However, others that prefer to live deep in the forest only reached their peak abundances more than 200 to 400 metres from the forest edges. These species seem to be dependent on large, continuous forests. If forests continue to be fragmented, these species may be driven out.

Roads everywhere

“It’s a tremendously important study, because it integrates such a large amount of data for nearly 2000 vertebrate species,” says of James Cook University in Queensland, Australia. “In some ways, it confirms our worst fears.”

Laurance emphasises that forests in tropical developing nations will be particularly affected by the fast pace of road-building there. In a paper published last week, he and his colleagues estimated that, of the projected 25 million kilometres of paved roads that will be built by 2050, about 90 per cent will be in these regions ().

“Roads typically open up a Pandora’s box of environmental problems for forest species,” says Laurance. The problems include fragmentation, hunting, logging, deforestation and illegal mining. In the Amazon, 95 per cent of all deforestation occurs within 5.5 kilometres of a legal or illegal road.

Many of these roads will be poorly built, so they will be washed away in heavy rainfall, or become riddled with holes. Rather than having a positive impact on development, .

Roads, and forest fragmentation in general, may also affect us – in a dramatic way. “Tropical forest edges are much more susceptible to wildfires,” says of Lancaster University, UK. A 2015 study found that , such as beside roads or clearings, striking there every 11 years compared with every 82 years in dense jungles. According to Barlow, preventing the fragmentation of forests may be a vital step in reducing the incidence of wildfires.

Changing climes

SHIPS spewing soot into the pristine ocean air are causing extra lightning strikes along busy maritime routes. It is a bizarre example of how human activities can change the weather.

When Joel Thornton at the University of Washington in Seattle and his colleagues looked at records of lightning strikes between 2005 and 2016 from the World Wide Lightning Location Network, they noticed there were significantly more strikes in certain regions of the east Indian Ocean and the South China Sea, compared with the surrounding areas. Unusually, they occurred along two straight lines in the open ocean, which coincided with two of the busiest shipping lanes in the world. Along these paths there were twice as many lightning strikes as in nearby areas.

“We were quite sure the ships had to be involved,” says Thornton. But they still had to eliminate other factors that influence storm intensity, such as wind speeds and temperatures.

Once these had been ruled out, the team concluded that aerosols from the ships’ engine exhausts were the culprit. Aerosol particles act as seeds, around which water vapour condenses into cloud droplets. In clean air there aren’t many seeds, so the cloud drops quickly grow and fall as rain.

But when there are a lot of seeds, like over busy shipping routes, a greater number of small cloud drops form. Since these are light, they rise up high into the atmosphere and freeze, creating clouds rich in ice.

It is this that leads to more intense thunderstorms: lightning only occurs if clouds are electrically charged, and this only happens if there are lots of ice crystals.

A key giveaway that aerosols were behind the effect was that the lightning was most pronounced at times of the year when powerful atmospheric convection currents form that can carry the aerosol particles high into the sky (Geophysical Research Letters, ).

Although lightning activity is higher over the shipping lanes, the amount of rainfall is no different to nearby regions.

While the study provides clear evidence that aerosol particles affect the development and intensity of storms, Thornton says it cannot be directly generalised to the air above land because there are other factors that need to be taken into account.

“Understanding this anthropogenic effect can help us predict future climate,” says Orit Altaratz Stollar of the Weizmann Institute of Science in Israel.

The study shows how the changes we make to the atmosphere affect clouds and even the development of stormy weather. Thornton also suggests that the pollution we have released over the last few hundred years may have affected storms and lightning in many places, creating lightning where there was none.

This article appeared in print under the headline “Cargo ships trigger lightning storms”

Adding a smattering of bacteria can help a laser beam travel further through murky water before it peters out. The finding could help us perform non-invasive medical diagnostics or image deep into tissue without causing any damage.

The presence of particles in a liquid normally causes light to scatter – that’s why your car headlights don’t penetrate far in dense fog. But when at San Francisco State University and colleagues shone a high-intensity green laser through seawater containing a cyanobacteria called Synechococcus, they found the light travelled further than they expected.

This boost is the result of a previously known effect: light exerts a force on the cells because their refractive index differs from that of the seawater they are sitting in. In this case, the force pulls the cells toward the centre of the light beam. Once there, another force causes the cells to align along the direction of the beam while also pushing them away from the centre.

This forms a bacteria “fibre” surrounding the beam, says Chen, which can act as a waveguide – constricting and guiding light travelling inside it. The effect lets the laser travel an extra few centimetres through the water.

Medical applications

The idea could be used to create environmentally friendly optical components that can be tailored to a range of applications, says Chen. “It may be possible to grow and fix biological waveguides and produce biological microchip technology.”

Despite being hit by a high-power laser, most of the cyanobacteria survived. The team is now studying whether human red blood cells can produce a similar waveguide effect and survive the process. If so, it would open the technique up to medical applications, such as imaging through biological fluids.

However, it remains to be seen whether this works in practice.

“A drawback is that the effect only occurs at very high laser power,” says , a biophysicist at Ulm University in Germany. This power level generally destroys mammalian cells, he says.

Cucumber seeds grown on board the International Space Station show an unusually strong tendency to grow towards water. This finding might help us engineer more drought-tolerant crops suitable for cultivation on Earth.

Plant growth is strongly influenced by the environment: stems grow up towards the sun, while roots grow down under the influence of gravity – an effect called gravitropism.

But in space, Earth’s gravitational pull is much less pronounced. Back in 1998, of Tohoku University, Japan, began investigating how plant roots behave in these unusual conditions. Through an experiment on the space shuttle Discovery, his team accidently discovered that roots bend if they grow in microgravity.

Takahashi and his colleagues wondered whether the roots were of their environment and so showing a “hydrotropic” response – growing towards water rather than with gravity. “The hypothesis is, in microgravity, the hydrotropic response will become pronounced,” he says.

To investigate further, the researchers sent cucumber seeds into space aboard the space shuttles Atlantis and Discovery in 2010. Japanese and US astronauts performed a series of experiments on the International Space Station, and the seedlings came back to Earth in 2011.

Onboard the ISS, the seeds were grown in a small chamber with wet filter paper on one side to set up a moisture gradient. Some of the seeds were allowed to grow in the ISS’s microgravity environment, others were grown inside a centrifuge to simulate Earth’s gravity.

Root around

The cucumber roots grown in microgravity bent towards the wet substrate, sometimes by as much as 60 degrees from the vertical. Those in conditions simulating Earth’s gravity grew vertically “downwards”.

Unexpectedly, the plant hormones – auxins – that encourage cucumber roots to grow downwards on Earth also seemed to encourage them to grow towards water in space. This suggests cucumber roots have a hidden ability to seek out water – but the power is masked on Earth because of their stronger response to gravity.

Takahashi thinks studying the hormone behaviour in more detail could prove productive. In the common, lab-grown plant Arabidopsis, the water-seeking behaviour of roots operates separately from gravity control, he says, and individuals with a stronger version of the water-seeking behaviour grow better in arid conditions.

If it is possible to separate the gravity and water-seeking behaviour of cucumber roots, we might be able to boost those water-seeking properties and grow cucumbers in drier conditions too.

of Tel Aviv University in Israel sees the potential benefits too. “I certainly believe that [with a better] understanding of the mechanisms governing hydrotropism and gravitropism, [it] will be possible to improve plant growth under water-deficient conditions,” he says.

Fromm adds that a stronger grasp of plant growth in space could prove beneficial on any off-planet colony.

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